In certain munitions applications, for example with warheads intended to penetrate thick walls such as bunkers or shelters, an impact delay fuze can be employed. This is a fuze which, on impact with the target, will initiate a delay element which will, in turn, allow the warhead to penetrate the wall before initiating the high explosive contents of the warhead. To operate properly the delay column must burn uniformly as the warhead decelerates through the thick target wall and then initiate the explosive train of the warhead.
The problems of designing a pyrotechnic delay that is capable of withstanding the high deceleration encountered on impact of a penetrating warhead are amplified where the delay unit must resist high acceleration on launch, as would be encountered where the warhead was fired from a gun. Additionally, the delay unit should be sized to fit inside the rotor of a safety and arming mechanism. Thus, the three main difficulties to be overcome in designing such a unit are:
1. the delay unit must be sized to fit inside the rotor of a safety and arming mechanism; PA1 2. the delay unit must sustain gun acceleration and be intact at impact on the target; and PA1 3. the delay unit must burn uniformly when the warhead decelerates through hard targets. PA1 a primer cavity; PA1 a delay cavity; PA1 a passage extending from the primer cavity to an upstream end of the delay cavity, the passage having a downstream end opening into the delay cavity that is substantially smaller in area than the upstream end of the delay cavity; and PA1 a detonator cavity adjoining the delay cavity at the downstream end thereof, the pyrotechnic train comprising: PA1 a primer in the primer cavity; PA1 a delay column filling the delay cavity; and PA1 a pellet of detonator composition filling the detonator cavity.